The present invention is in the field of downhole tools and particularly relates to apparatus for protecting areas of such tools from abrasion, erosion or wear.
An example where the protection of a downhole tool from such defeating is important is the gauge of a drill bit. Drill bit crowns (or drill heads) typically comprise an end face with a cutting structure and a gauge behind the cutting structure. The purpose of the gauge area on a drill bit is to support the bit in the bore hole, previously drilled by the cutting structure on the end face of the crown. This serves to keep the drill bit crown concentric to the bore hole axis and maintains stability, thereby preventing resonant vibrations and other complex motion.
It will be appreciated by those skilled in the art that in the event that the gauge of the drill head becomes deformed or otherwise defaced through wear or abrasion, the integrity of the bore hole is diminished. Clearly it is important for a drill bit to retain its shape if the tool string to which it is attached is to be operated successfully.
Other down-hole equipment, such as stabilisers and casing centralisers also become far less effective if they are deformed or otherwise defaced. As the dimensional integrity of a stabiliser is diminished it is less able to control the steerability of a downhole tool string.
An object of the present invention is therefore to provide a means for strengthening or hardening areas of downhole tools or other apparatus in order to increase their resistance against abrasion, erosion or wear.
In the past drill bits are most commonly protected by reinforcing the gauge. This is usually done by impregnating the drill bit with a relatively hard material that supports the external structure of the gauge. Such materials, for descriptive purposes, may be classified into xe2x80x9chardxe2x80x9d and xe2x80x9csuper hardxe2x80x9d materials. Hard materials comprise materials such as tungsten carbide, while thermally stable product (TSP) and natural diamond provide examples of super hard materials.
These strengthening materials are generally not used to form the structure of the down hole component, being difficult to machine and expensive. It is therefore desirable to impregnate the surface of an existing down-hole structure with the hard or super hard materials. In the case of hard materials, this can be achieved by welding particles of the hard material on to the surface of the down hole apparatus and then spray fusing a binding material around the particles. Subsequent grinding or other material removal operations then enable the gauge or other surface area to be finished to specified dimensions.
However, this process has not been considered as appropriate in the past in respect of super hard materials, owing to the general rule that super-hard materials are not electrical conductors and therefore not suited to spot welding.
Not only are super hard materials advantageous in view of their additional hardness, but they also tend to be superior in respect of their tolerance to the hot temperatures encountered down-hole. Yet, although super hard materials are clearly more desirable for use in protecting down-hole surfaces from wear than are hard materials, conventionally it is necessary to braze in the super hard components. This is both time consuming and expensive.
It is therefore recognised in the present invention that it would be desirable to strengthen the surfaces of down-hole components with TSP or other super hard materials using a technique other than brazing.
In order to achieve a solution in response to this recognition, an object of the present invention is to identify a means for holding super hard materials to a surface of a down hole tool temporarily while a more permanent securing or anchoring means is applied.
A yet further object of the present invention is to provide a method for holding the super hard material onto the area to be protected prior to the application of a binder material. Preferably this would be achieved in a manner that allows for a specific pattern of location for the super hard material; the pattern being maintainable during the subsequent binder process.
According to the present invention, there is provided a method for protecting the surfaces of down-hole tools and drilling apparatus, the method comprising the steps of:
a) fixing a super hard material to the surface of the down-hole tool at least temporarily prior to spray fusing; and
b) Spray fusing a binding material around the super-hard material in order to provide a permanent binding medium for the super hard material to the surface of the tool.
Preferably the super hard material is affixed to the surface of the down-hole tool using a high temperature adhesive.
Preferably the high temperature adhesive is applied to the super hard material by the use of a syringe.
Alternatively, the super hard material is bathed in the high temperature adhesive prior to affixing said super hard material to the downhole tool surface.
Alternatively, the high temperature adhesive is brushed onto the surface of the down hole tool.
Preferably the high temperature adhesive is alumina based.
Preferably the high temperature adhesive has the consistency of a paint or paste.
Preferably the high temperature adhesive is a curing adhesive.
The super hard material may also be held within a mesh framework, wherein the framework is fixed to the surface of the downhole tool using a high temperature adhesive.
Alternatively, the super hard material is affixed to the surface of the down hole tool by welding, wherein the super hard material is combined with an electrically conductive component to facilitate welding.
Typically the welding of the electrically conductive component will be spot welding using electrical resistance techniques well known to persons skilled in the art.
The electrically conductive component may be a coating on the super hard material. It may for example comprise of a nickel, copper or chromium based alloy that is applied to the super hard material by electroplating.
Alternatively, the electrically conductive component may be a metallic substrate having locating means for holding the super hard material in place during the spray fusing process. Yet further, the electrically conductive component may be a metal framework, preferably in mesh form. The framework may similarly be used to locate small cubes or other shaped particles of the super hard material until such are permanently anchored by means of the application of the surrounding binder material.
The invention is not limited to the order in which the super hard material is fixed to the down hole tool. That is to say, where the electrically conductive component is a metallic substrate or framework for example, the substrate or framework may be affixed to the surface of the tool prior to the attachment thereto (or location therewith) of the super hard material. Alternatively, the substrate may be combined with the super hard material before the substrate is attached to the tool surface.
The down hole tool may be drill bit, reamer shoe or stabiliser or similar device used in applications inside bore holes. Generally, the invention finds application in relation to any down hole tool having a metallic surface that is prone to wear, abrasion or erosion.
The super hard material may be thermally stable product, polycrystalline diamond composite or natural diamond. Other super hard materials will be known or may become known to those skilled in the art and may also find application in respect of this invention.
According to a second aspect of the present invention there is provided a down hole tool having at least part of its surface being toughened against wear or other attack by the inclusion of a super hard material.
Preferably the super hard material is thermally stable product (TSP).
Typically, the down hole tool will be a drill bit.